The present invention relates generally to digital communication networks, and more specifically, to Fibre Channel transport over a SONET path.
SONET/SDH and optical fiber have emerged as significant technologies for building large scale, high speed, Internet Protocol (IP) based networks. SONET, an acronym for Synchronous Optical Network, and SDH, an acronym for Synchronous Digital Hierarchy, are a set of related standards for synchronous data transmission over fiber optic networks. SONET/SDH is currently used in wide area networks (WAN) and metropolitan area networks (MAN). A SONET system consists of switches, multiplexers, and repeaters, all connected by fiber. The connection between a source and destination is called a path.
One network architecture for the interconnection of computer devices in network communication is Fibre Channel, the core standard of which is described in ANSI (American National Standards Institute) X3.230-1994. Arising out of data storage requirements, Fibre Channel currently provides for gigabit-per-second transport over distances up to 10 kilometers in Fibre Channel frames that consist of standardized sets of bits used to carry data over the network system.
To combine the advantages of the SONET/SDH and Fibre Channel technologies, it is desirable to provide Fibre Channel transport over SONET/SDH networks, i.e., to map one or more Fibre Channel ports to a SONET/SDH path for transport across a SONET/SDH network. With a Fibre Channel transport over SONET/SDH product at each end of a SONET/SDH path, a method is needed for the Fibre Channel over SONET/SDH transport path to behave transparently so that its behavior emulates a direct Fibre Channel connection between end stations connected to the Fibre Channel over SONET/SDH equipment. In order to do this, a Fibre Channel port at one end of a SONET/SDH transport path must be able to bring down its link when the corresponding Fibre Channel port at a second end of the SONET/SDH path is down, i.e., unable to transmit or receive data, or when the SONET/SDH path is not operable.
Heretofore, the only method of determining whether a remote port or network node was down has been through layer 2 connection level protocols, such as PPP (Point-to-Point Protocol) signaling. However, such connection level protocols are burdensome because these protocols must be implemented at each port or node, resulting in additional and undesirable overhead. In fact, there is no PPP protocol for Fibre Channel. Higher level protocols, such as SCSI, are required to handle this operation for Fibre Channel. Such arrangements may be inefficient since several send frame sequence retries may be required before an upper level protocol time limit is reached and the upper level protocol recognizes that a remote port or node is down. Furthermore, such arrangements interfere with the ability for ISLs (interswitch links), which are trunk connections between Fibre Channel switches consisting of multiple links, to be reconfigured so that resources may be reallocated to different links.
The Fibre Channel transport over SONET/SDH networks should also be resilient to SONET/SDH protection switches (i.e., from UPSR, BLSR, etc.), within the path which can cause traffic disruption. In order to do this, the implementation should provide for minimal frame loss during SONET switches. Also, it should not bring down links during a SONET switchover unless there is a permanent failure condition within the SONET transport path.